Determination of unbound docetaxel and paclitaxel in plasma by ultrafiltration and liquid chromatography-tandem mass spectrometry

This work describes the development of a straightforward method for the determination of free docetaxel and paclitaxel in plasma. The separation of bound and unbound drug was performed with ultrafiltration. Different ultrafiltration devices were evaluated, especially regarding non-specific binding to the device. The most appropriate device for this application was selected and a procedure to counteract non-specific binding to the ultrafiltrate collection cup was developed. This consisted of a wash procedure with methyl t-butyl ether. A liquid/liquid extraction with methyl t-butyl ether was performed and samples were analysed with a previously developed liquid chromatography-tandem mass spectrometry procedure. The method used a Merck Purospher Star RP-18 column (55 mm x 2.0 mm, 3-microm particle size) and electrospray in the positive mode. A triple quadrupole instrument was used to monitor MRM transitions. Small modifications to this procedure were made to ensure adequate sensitivity. Within- and between-day reproducibility did not exceed 15% and accuracy ranged between 94.4 and 102.5%. The calibration range of the method was from 0.4 to 100 ng/ml both for paclitaxel and docetaxel. Finally, a fast and relatively simple method could be developed.     

Characterization of N-glycans of recombinant human thyrotropin using mass spectrometry

Thyroid-stimulating hormone is a vital component of the regulatory mechanism that maintains the structure and function of the thyroid gland and governs thyroid hormone release. In this paper we report the first detailed structural characterization of the N-linked oligosaccharides of recombinant human thyroid-stimulating hormone (rhTSH). Using a strategy combining mass spectrometric analysis and sequential exoglycosidase digestion, we have defined the structures of the N-glycans released from recombinant human thyrotropin by peptide N-glycosidase F. All glycans are complex-type glycans and are mainly of the bi- and triantennary type with variable degrees of fucosylation and sialylation. The major non-reducing epitope in the complex-type glycans is: NeuAcalpha2-3Galbeta1-4GlcNAc (sialylated LacNAc). The carbohydrate microheterogeneity at the three glycosylation sites was studied using reversed-phase high-performance liquid chromatography (RP-HPLC), concanavalin A affinity chromatography and mass spectrometric techniques, including both matrix-assisted laser desorption/ionization (MALDI) and electrospray. rhTSH was reduced, carboxymethylated and then digested with trypsin. The mixture of peptides and glycopeptides was subjected to RP-HPLC and the structures of the glycopeptides were determined by MALDI in conjunction with on-target exoglycosidase digestions. After PNGase F digestion, the peptide moiety of the glycopeptide was determined by the presence of the b- and y-series ions derived from its amino acid sequence in the quadrupole time-of-flight tandem mass (QTOF-MS/MS) spectrum. Glycosylation sites Asn-alpha52 and Asn-alpha78 contain mainly bi- and triantennary complex-type glycans. Only glycosylation site Asn-alpha52 bears fucosylated N-glycans. Minor tetraantennary complex structures were also observed on both glycosylation sites. Profiling of the carbohydrate moieties of Asn-beta23 indicates a large heterogeneity. Bi-, tri-, and tetraantennary N-glycans were present at this site. These data demonstrate site-specificity of glycosylation in the alpha subunit but not in the beta subunit of rhTSH with Asn-alpha52 bearing essentially di- and triantennary glycans with or without core fucosylation and bi- and triantennary glycans with no core fucosylation being attached to Asn-alpha78.     

Governance implications of nanomaterials companies’ inconsistent risk perceptions and safety practices

Current research on the nanotechnology industry indicates its downstream expansion at a rapid pace, while toxicological research and best practices for environmental health and safety are still being developed. Companies that use and/or produce engineered nanomaterials (ENMs) have enormous potential to influence safe-handling practices for ENMs across the product life cycle. Knowledge of both industry practices and leaders’ perceptions of risk is vital for understanding how companies will act to control potential environmental and health risks. This article reports results from a new international survey of nanomaterials companies in 14 countries. In this survey, company participants reported relatively high levels of uncertainty and/or perceived risk with regard to ENMs. However, these perspectives were not accompanied by expected risk-avoidant practices or preferences for regulatory oversight. A majority of companies indicated “lack of information” as a significant impediment to implementing nano-specific safety practices, but they also reported practices that were inconsistent with widely available guidance. Additionally, in the absence of safe-handling regulations, companies reported nano-specific health and safety programs that were narrow in scope. Taken together, these findings indicate that health and safety guidance is not reaching industry. While industry leaders’ reluctance toward regulation might be expected, their own reported unsafe practices and recognition of possible risks suggest a more top-down approach from regulators is needed to protect workers and the environment.     

Economical Access to Diverse Enantiopure Tetrahydropyridines and Piperidines Enabled by Catalytic Borrowing Hydrogen

We disclose herein a catalytic borrowing hydrogen method that enables an unprecedented, economical one-pot access to enantiopure tetrahydropyridines with minimal reagent use or waste formation. This method couples a few classes of readily available substrates with commercially available 1,3-amino alcohols, and delivers the valuable tetrahydropyridines of different substitution patterns free of N-protection. Such transformations are highly challenging to achieve, as multiple redox steps need to be realized in a cascade and numerous side reactions including a facile aromatization have to be overcome. Highly diastereoselective functionalizations of tetrahydropyridines also result in a general access to enantiopure di- and tri-substituted piperidines, which ranks the topmost frequent N-heterocycle in commercial drugs.     

Not So Innocent After All: Interfacial Chemistry Determines Charge-Transport Efficiency in Single-Molecule Junctions

Most studies in molecular electronics focus on altering the molecular wire backbone to tune the electrical properties of the whole junction. However, it is often overlooked that the chemical structure of the groups anchoring the molecule to the metallic electrodes influences the electronic structure of the whole system and, therefore, its conductance. We synthesised electron-accepting dithienophosphole oxide derivatives and fabricated their single-molecule junctions. We found that the anchor group has a dramatic effect on charge-transport efficiency: in our case, electron-deficient 4-pyridyl contacts suppress conductance, while electron-rich 4-thioanisole termini promote efficient transport. Our calculations show that this is due to minute changes in charge distribution, probed at the electrode interface. Our findings provide a framework for efficient molecular junction design, especially valuable for compounds with strong electron withdrawing/donating backbones.     

Synthesis and properties of new phosphorus-functionalized bithiophene materials

The synthesis and reactivity of the novel dithieno[3,2-b:2′,3′-d]-phosphole system and its potential use in polymeric sensory materials was investigated. Due to the nucleophilic nature of the phosphorus atom, these materials were found to be easily tunable. Classical reactions at the phosphorus center were performed to modify the electronic structure of the system and the corresponding changes were detected by UV/Vis and fluorescence spectroscopy. Depending on the oxidation state of the central phosphorus atom or its substitution pattern, the dithieno[3,2-b:2′,3′-d]-phospholes show varying wavelengths for absorption and emission allowing to distinguish between different compounds by means of optical spectroscopy.     

The Stokesian Dynamics Method and the Settling behaviour of Particle-Fibre-Mixtures

Sedimentation of fibres and particles can be observed manifold in industrial application. In waste water treatment, the water is clarified from solid particles and fibres utilizing sedimentation. Some filtration processes use fibres as an aid to improve the filtration quality. Finally, in the paper recycling process, one tries to separate cellulose fibres from inorganic particles used as filling material or in printing colours. For all these applications, it is necessary to understand the hydrodynamic interactions between single particles as well as particle and fibre collectives. In the present paper, the sedimentation behaviour of fibres and particles is considered in detail. Mathematic modelling is used to investigate inter particle influences in detail. In particular, a method called Stokesian Dynamics is used to simulate the settling of fibres and particles. The main challenge of the modelling is the dependence of the direction of each fibre on its sedimentation velocity and the different sizes of the particles in a poly-modal particle size distribution. Additionally fibres, particles and the fluid are influencing each other in a significant manner and in a long range. Therefore, while calculating the force on a particle, one has to take into account the influences of many particles. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)